JPH053056B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a lens driving device for a pickup section in an optical information reading device.

BACKGROUND ART An optical information reading device irradiates a recording track formed on an information recording surface of a recording medium with a focused information reading laser beam as a spot light, detects a change in reflected light from the information recording surface, and reads information. This is the reading. To achieve this, it is necessary to always focus the information reading laser beam onto the recording track despite the surface wobbling caused by the warping of the recording medium surface. The lens is configured so that focus adjustment (focus servo) can be performed by minutely moving the lens in a perpendicular direction. In addition, since it is necessary for the laser beam to always accurately track the recording track despite the eccentricity of the recording track, it is also possible to move the objective lens minutely in a direction perpendicular to the recording track (tracking servo). It is configured.

A lens driving device shown in FIGS. 5 and 6 for moving such an objective lens has already been developed by the applicant. In the already developed lens driving device, as shown in FIG. 5, an objective lens 1 for irradiating a recording surface of a recording medium (not shown) with spot light is attached to a lens holder 2. The lens holder 2 has a hollow portion 3 formed therethrough. One focusing coil 4 and two tracking coils 5 are fixed in the hollow part 3. The focusing coil 4 is fixed so that its central axis is parallel to the optical axis of the objective lens 1, and the tracking coil 5 is fixed so that its central axis is perpendicular to the optical axis of the objective lens 1. It is attached to the outer peripheral surface of the single coil 4. The lens holder 2 to which the following coil 4, the tracking coil 5, and the objective lens 1 are fixed includes a cantilever-shaped 4-piece extending in a direction perpendicular to the optical axis direction of the objective lens 1.
It is attached to the free end of the book support member 6. On the other hand, a fixed end portion of the support member 6 is fixed to the base 7. Since the four supporting members 6 are flexible, the lens holder 2 is movable in the optical axis direction of the objective lens 1 (arrow F direction) and in the direction perpendicular to the optical axis direction (arrow T direction). It is becoming. however,
This movement is relative to base 7.

In the hollow part 3 of the lens holder 2, which is supported movably in two directions with respect to the base 7 in this way,
A magnet 8 and a yoke 9 are inserted therein to generate a magnetic flux that interlinks with the focusing coil 4 and tracking coil 5 fixed therein. The magnet 8 and the yoke 9, preferably made of a ferromagnetic material, constitute a magnetic circuit which includes a single magnetic gap 1 producing parallel magnetic flux.
0 is set. Magnet 8 and yoke 9
is a focusing coil 4 in a magnetic gap 10.
The tracking coil 5 is inserted into the hollow portion 3 of the lens holder 2 so that one side of the tracking coil 5 is positioned as the active sides 4a and 5a. The acting sides 4a and 5a herein refer to electromagnetic forces acting in the directions of arrows F and T, respectively, within the magnetic gap 10 where parallel magnetic flux exists when current is supplied to the focusing coil 4 and tracking coil 5. This means a portion of each coil 4,5. The magnet 8 and yoke 9 inserted into the hollow portion 3 as described above are attached to a fixing member (not shown) fixed within the base 7.

In the lens driving device configured as described above, the objective lens 1 can be driven together with the lens holder 2 in the direction of arrow F by supplying current to the focusing coil 4, and the tracking coil 5
By supplying current to , the objective lens 1 and the lens holder 2 can be driven in the direction of arrow T.

SUMMARY OF THE INVENTION An object of the present invention is to improve the lens drive device as described above and provide a lens drive device that is lighter and more efficient.

In the lens driving device according to the present invention, the magnetic circuit is provided with a magnetic gap that generates first and second magnetic fields in mutually opposite directions, and within the magnetic gap are two oppositely facing focusing coils and a tracking coil. Only the sides are disposed, and the proportions of the lengths of the two sides extending within the first and second magnetic fields are inversely proportional.

Embodiments Hereinafter, embodiments of the present invention will be described in FIGS. 1 to 4.
This will be explained with reference to the drawings up to the figure. In addition, by assigning the same symbols to the same parts as those used in the already developed lens drive device explained in the "Background technology" section,
Explanation of the same parts will be omitted.

FIG. 1 shows a lens driving device according to the invention. In this lens driving device, Fig. 3a
and a magnet 18 facing a single magnetic gap 10 provided in the magnetic circuit, as shown in FIG.
The side surfaces of the magnet are magnetized with N and S poles. Therefore, first and second magnetic fields are generated in the magnetic gap 10 in opposite directions. The magnetic circuit is provided so that the directions of the first and second magnetic fields are perpendicular to the movement plane of the lens holder 2 along the arrow F direction and the arrow T direction.

On the other hand, both the focusing coil 14 and the tracking coil 15 are connected to the hollow part 3 of the lens holder 2.
It is pasted onto the bobbin 21 fixed inside. The central axes of these coils substantially coincide and coincide with the direction of the magnetic field.

Under the above-mentioned configuration, a focusing coil 14 and a tracking coil 1 are provided in the magnetic gap 10.
Only two opposing sides of each of the focusing coils 14 extend, and the two opposing sides of the focusing coil 14 are arranged at right angles to the two opposing sides of the tracking coil 15.

The ratio of the lengths of the two opposing sides of each coil 14, 15 extending within the first and second magnetic fields is inversely proportional, as shown, for example, in FIGS. 3a and 3b. In particular, the magnet 1 shown in Figure 3a
In the case of 8, the N pole and S pole magnetized on the side
A line segment whose center is a point where the polar boundary line is perpendicular to the coil center axes of both coils 14 and 15 and intersects with the center axes, and a line segment extending in opposite directions from both ends of the line and focusing coil 14 or tracking coil 1.
It is a crank-shaped boundary line formed by two opposing sides of 5 and a perpendicular half line. It is preferable to set the magnetization pattern of the magnet 18 as shown in FIG. 3a, since it is possible to prevent rotational moment caused by a driving force from acting on the lens holder 2 as described later.

Next, the operation of the lens driving device according to the present invention will be explained. In FIG. 4a, when a current is supplied to the focusing coil 14, the two opposing sides extending within the magnetic gap 10 of the focusing coil 14 have one side within the first magnetic field and the other side within the magnetic gap 10. Since it extends only within two magnetic fields, electromagnetic force P in the same direction acts uniformly on the two sides as shown. This electromagnetic force drives the lens holder 2 in the direction of arrow F. On the other hand, since the proportions of the lengths of the two opposing sides of the tracking coil 15 extending in the first and second magnetic fields extending in the magnetic gap 10 are inversely proportional to each other, in FIG. For example, when a current flowing clockwise is supplied to the tracking coil 15, the electromagnetic force P acting on the two sides has a distribution as shown in the figure. In this case, the lens holder 2 is driven in the direction of arrow T by the resultant force of the electromagnetic forces P. By the way, in FIG. 4b, when looking at the distribution of the electromagnetic force P acting on each of the two sides, a rotational moment acts only on each side. However, since the rotational moments acting on each of the two sides are equal in strength and act in opposite directions, they cancel each other out. That is, this is preferable because no rotational moment acts on the lens holder 2, and efficient and smooth driving can be performed.

Effects of the Invention As explained above, in the lens driving device according to the present invention, only the two opposing sides of the focusing coil and the tracking coil are placed in the magnetic gap having the first and second magnetic fields in opposite directions. are arranged, and the proportions of the lengths of the two sides extending within the first and second magnetic fields are inversely proportional.
With this structure, compared to previously developed lens drive devices in which only one side of each coil is placed in the magnetic gap as an active side, It is possible to increase the length of the part (action side) that extends over the area and receives electromagnetic force. Therefore, greater driving force can be obtained with less electric power, improving efficiency. Furthermore, since the number of turns of each coil can be reduced, a lightweight and compact lens driving device can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a lens driving device according to the present invention, FIG. 2 is a diagram showing the relationship between each coil and a magnetic circuit in the lens driving device according to the present invention, and FIG. 3 is a diagram showing the relationship between the magnet 18 and each coil in the present invention. Figure 4 is a diagram showing the distribution of electromagnetic force acting on each coil, Figure 5 is a diagram showing a previously developed lens drive device, and Figure 6 is a diagram showing a previously developed lens drive device. The figure which showed the relationship between each coil and the magnetic circuit in a device. Explanation of symbols of main parts, 1...Objective lens, 2
... Lens holder, 10 ... Magnetic gap, 14
...Focusing coil, 15...Tracking coil.

Claims (1)

[Claims] 1. An objective lens for irradiating a recording surface of an optical recording medium with spot light and a lens holder for holding the objective lens are movable in the optical axis direction of the objective lens and in a direction perpendicular thereto, and A lens driving device including a support mechanism that supports the optical axis so that it is perpendicular to the recording surface, and a driving means that drives the lens holder, wherein the driving means is perpendicular to the lens holder movement surface. a magnetic circuit having a single magnetic gap producing first and second magnetic fields in opposite directions;
a first coil and a second coil having only two opposing sides disposed within the magnetic gap;
The two opposite sides of the coil are arranged at right angles to the opposite sides of the second coil, and the two opposite sides of each of the first and second coils have length ratios that are inversely proportional to each other. A lens driving device extending within the first and second magnetic fields.